Drupal 7 Module Development

Building an Admin Interface
This is the same Form API element we created above, but with a new line added.
This line adds the '#default_value' property of the form element. This property
tells the form what data the element should contain when the form is first loaded.
We are assigning this property the results of a call to variable_get() using two
parameters. The first parameter is the unique key associated with this data. It is
common practice to give a persistent variable the same name as the form element
it is associated with, and we have done so here.
Like menu items, persistent variables are cached by Drupal, so you
will often need to clear your caches after modifying them.
The second parameter specifies the data that should be returned if this variable
has never been explicitly set. In this example we have set that to be the string
'Administrative Warning'. If this variable had been explicitly set sometime
previously, then that data will be returned by variable_get() instead. Otherwise,
the default value will be returned.
Now the first time the form loads, whatever data is in the persistent variable
'user_warn_e-mail_subject' will be set as the value of the e-mail subject form
element. We can also do this to our other form elements as desired. In the end our
function will be as follows. Note that we have also added a constant containing the
default text of our e-mail. Removing this large block of text from our array definition
makes our code more readable and maintainable down the road.
Drupal constants are typically defined at the top of a .module file, but for the sake
of clarity this example includes the constant definition with the function:
define('USER_WARN_MAIL_TEXT',
'Hello,
We have been notified that you have posted comments on our site that
are in violation of our terms of service. If this behavior continues
your account will be suspended.
Sincerely,
The administrative staff');
function user_warn_form($form, &$form_state) {
$form = array();
// Text field for the e-mail subject.
$form['user_warn_e-mail_subject'] = array(
'#type' => 'textfield',
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